JP3578801B2 - Receiver - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a receiving apparatus used for an orthogonal frequency division multiplexing (OFDM), which is a modulation scheme suitable for terrestrial digital television broadcasting or digital audio broadcasting.
[0002]
[Summary of the Invention]
The present invention relates to a receiver in a multi-valued orthogonal frequency division multiplexing (OFDM) system, which is one type of a multicarrier digital modulation system, and has amplitude / phase reference data serving as a reference for amplitude / phase on a transmission side. Is periodically transmitted at a predetermined position in the transmission frame, and when the receiving device restores the valid data based on the amplitude / phase reference data, a plurality of received amplitude / phase reference data Based on the amplitude value fluctuation, the magnitude of the phase value fluctuation and its fluctuation rate, etc., it is detected whether the receiving device is stopped or moving, and whether the transmission line characteristic is stationary or non-stationary. When detecting the reference data for demodulation based on these detection results, a plurality of received amplitude / phase reference Data by calculating the average value of the data or by calculating the interpolation value, and by averaging, by adjusting the number of averages (the number of averaged amplitude and phase reference data) It is possible to always optimize the value of the reference data for demodulation according to the receiving condition of the receiving device, the characteristic change of the transmission path, and the like.
[0003]
[Prior art]
A transmission / reception system using an orthogonal frequency division multiplexing (OFDM), which is a modulation system suitable for terrestrial digital television broadcasting or digital audio broadcasting, is disclosed, for example, in Japanese Patent Application Laid-Open No. 05-219021. Japanese Patent Application Publication No. 04-017067) discloses an "orthogonal frequency division multiplexing digital signal transmission system and a transmitting device and a receiving device used for the same".
[0004]
In this transmission / reception system, a plurality of signals to be transmitted (valid data) and amplitude / phase reference data (reference data) are set as complex data on the frequency axis by a transmitting device, and these complex data are subjected to inverse discrete Fourier transform. To generate a baseband time-axis waveform on the time axis to generate an OFDM signal, which is transmitted at a radio frequency.
[0005]
Then, the receiving device receives the OFDM signal, reproduces the baseband time-axis waveform, performs a discrete Fourier transform on the baseband time-axis waveform, and calculates the value of each signal based on the value of the reference data obtained thereby. And reproduces the received signal contained in the OFDM signal.
[0006]
[Problems to be solved by the invention]
However, such an orthogonal frequency division multiplex digital modulation method has the following problems.
[0007]
First, in such an orthogonal frequency division multiplex digital modulation scheme, when restoring valid data based on reference data, the latest demodulation reference data used for restoring the valid data is obtained as the demodulation reference data obtained by the reception operation. When one piece of reference data is used, in principle, the bit error rate characteristics of the demodulated received data should be substantially the same as the bit error rate characteristics in the case of differential detection in the single carrier digital modulation method. it can.
[0008]
However, the receiving apparatus using such an orthogonal frequency division multiplexing digital modulation method is not always fixed at a fixed location, and the transmission path characteristics are not always constant, In an actual receiving apparatus, when one latest reference data obtained by the receiving operation is used as demodulation reference data used for restoring valid data, the bit error rate characteristic of the demodulated reception data is simply There is a problem that the bit error rate becomes worse than the bit error rate characteristic in the case of differential detection in the one carrier digital modulation method.
[0009]
Therefore, in order to eliminate such inconveniences, as a method of obtaining demodulation reference data, a plurality of reference data obtained by the reception operation are averaged so that an optimum value is always obtained as the value of the demodulation reference data. Thus, the bit error rate is reduced even when one receiver is used in a fixed state, in a portable state, in a mobile state, or when the transmission line characteristics fluctuate greatly. It is thought to make it.
[0010]
However, in the method of averaging a plurality of reference data obtained by the reception operation to obtain the value of the demodulation reference data, only the demodulation reference data is temporally averaged. When the amplitude or phase of the received data changes with the passage of time, for example, when the receiving apparatus is moved and received, or when the characteristics of the transmission path change suddenly, the bit error rate is rather deteriorated. There was such a problem.
[0011]
In view of the above circumstances, the present invention can always obtain an optimum value as the value of the demodulation reference data regardless of the condition of the reception mode or the fluctuation state of the transmission path, and thereby, the bit of the reception data can be obtained. It is an object of the present invention to provide a receiving device capable of greatly reducing an error rate.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an orthogonal frequency division method for generating a multicarrier signal by expanding a plurality of transmission data to be transmitted on a frequency axis and then expanding the transmission data on a time axis in claim 1 A receiving device in a multiplex modulation / demodulation method, wherein effective data is restored from a transmitting side based on amplitude / phase reference data which is inserted at a predetermined position in a transmission frame and periodically transmitted as an amplitude / phase reference. Means for calculating at least one of an average value or an interpolated value of the received plurality of amplitude / phase reference data to obtain reference data for demodulation used for restoring valid data; Receiving state detecting means for detecting whether the receiving apparatus is stationary or moving, or whether the receiving apparatus is stationary or moving, and based on a detection result obtained by the receiving state detecting means. Means for switching whether to obtain demodulation reference data used for restoring data by calculating an average value of a plurality of received amplitude / phase reference data or by calculating an interpolation value. It is characterized by:
[0013]
According to a second aspect of the present invention, in the receiving apparatus according to the first aspect, the fluctuation rate detecting unit detects a change speed of a transmission path characteristic or an approximate value of a moving speed of the receiving apparatus, and the fluctuation rate detecting unit obtains the fluctuation rate detecting unit. Means for obtaining demodulation reference data used for restoring valid data by changing the number of reference data to be averaged when calculating an average value of a plurality of received amplitude / phase reference data based on a detection result It is characterized by having.
[0019]
[Action]
According to the above configuration, the value of the reference data for demodulation is always set to an optimal value regardless of the condition of the reception mode or the fluctuation state of the transmission line, thereby greatly reducing the bit error rate of the received data. Can be done.
[0026]
【Example】
<< Basic principle of receiving apparatus according to the present invention >>
First, when the receiving apparatus is fixed and received, if there is little change in transmission path characteristics, the average value of the plurality of received reference data is calculated and used as the average value of the demodulation reference data. Ask for data.
[0027]
As a result, the bit error rate characteristics of the demodulated received data can be made closer to the bit error rate characteristics in the case of synchronous detection in the single carrier digital modulation method.
[0028]
However, if such averaging processing of the reference data is performed during mobile reception, the bit error rate is rather deteriorated.
[0029]
Therefore, when the receiving apparatus is moved and received or when the change in the transmission path characteristics is large, the latest reference received before the time is used as the reference data for demodulating the valid data received at a certain time. A value obtained by interpolating the data and the reference data first received after the time is used.
[0030]
As a result, the bit error rate characteristics of the demodulated received data can be made closer to the bit error rate characteristics in the case of synchronous detection in the single carrier digital modulation method.
[0031]
In view of the above, in the present invention, the receiving apparatus is used in a fixed reception mode or a portable / mobile reception mode, and the transmission path is in a stable or unstable state. Depending on the receiving conditions, when determining the demodulation reference data from multiple reference data, select the best one of the averaging process or interpolation process, and optimize the number of reference data to be used when averaging. Therefore, an optimum value can be always obtained as the value of the reference data for demodulation, regardless of the condition of the receiving apparatus or the fluctuation state of the transmission path, thereby greatly increasing the bit error rate of the received data. To reduce it.
[0032]
<< Configuration of Example >>
<Description of configuration of transmitting device>
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0033]
FIG. 1 is a block diagram illustrating an example of the transmission device.
[0034]
The transmission apparatus 1 shown in FIG. 1 includes a fixed reference data memory circuit 2, a timing generation circuit 3, a valid data / reference data switching control circuit 4, a switching switch 5, a serial / parallel conversion circuit 6, an OFDM modulation circuit 7, And a frequency conversion circuit 8 for sequentially taking in a plurality of valid data to be transmitted and inserting reference data having a preset amplitude value and phase value into a predetermined portion of each of the valid data. After that, the data is converted into parallel complex number data, which is further subjected to inverse discrete Fourier transform to obtain a baseband time axis waveform of the OFDM signal, and then the baseband time axis waveform is converted into a radio frequency OFDM signal and transmitted.
[0035]
The fixed reference data memory circuit 2 stores a fixed value of the reference data in advance, and supplies the reference data having the registered unique value to one terminal of the changeover switch 5.
[0036]
Further, the timing generation circuit 3 oscillates at a preset frequency to generate a frame synchronization signal, a symbol synchronization signal, a carrier wave number count pulse signal, a sampling clock signal, and the like. And the OFDM modulation circuit 7.
[0037]
The valid data / reference data switching control circuit 4 forms each OFDM signal transmission frame based on a frame synchronization signal, a symbol synchronization signal, a carrier wave number count pulse signal, a sampling clock signal, and the like output from the timing generation circuit 3. A control signal required to insert reference data into a carrier wave satisfying a preset condition among carrier waves of transmission symbols is generated and supplied to the changeover switch 5.
[0038]
The changeover switch 5 receives reference data output from the fixed reference data memory circuit 2 by one terminal, receives valid data to be transmitted by the other terminal, and outputs from the valid data / reference data switching control circuit 4. When the control signal to be specified specifies valid data, the valid data input to the other terminal is selected and supplied to the serial / parallel conversion circuit 6, and the control signal specifies reference data. The reference data input to one terminal is selected and supplied to the serial / parallel conversion circuit 6.
[0039]
The serial / parallel conversion circuit 6 takes in the reference data and valid data output from the changeover switch 5 and serial / parallel converts the reference data and effective data into a plurality of complex data respectively corresponding to each carrier constituting the OFDM signal. Is supplied to the OFDM modulation circuit 7.
[0040]
The OFDM modulation circuit 7 converts each complex number data output from the serial / parallel conversion circuit 6 based on a frame synchronization signal, a symbol synchronization signal, a carrier number count pulse signal, a sampling clock signal, etc., output from the timing generation circuit 3. At the same time, each of these complex data is subjected to an inverse discrete Fourier transform to convert each of these complex data on the frequency axis into a baseband time axis waveform (or intermediate frequency) on the time axis, and then Is supplied to the frequency conversion circuit 8.
[0041]
The frequency conversion circuit 8 takes in a baseband time axis waveform (or an intermediate frequency) output from the OFDM modulation circuit 7, converts it into a radio frequency, generates an OFDM signal to be a transmission signal, and transmits this. .
[0042]
<Description of operation of transmitting device>
Next, the operation of the transmitting apparatus 1 will be described with reference to the block diagram shown in FIG.
[0043]
First, valid data to be transmitted is fetched and supplied to the changeover switch 5, and a fixed value of reference data registered in advance is read out by the fixed reference data memory circuit 2, and this is read by the changeover switch 5. Supplied to
[0044]
The output timing of the reference data is determined by the valid data / reference data switching control circuit 4 based on the frame synchronization signal, the symbol synchronization signal, the carrier wave number count pulse signal, the sampling clock signal, and the like output from the timing generation circuit 3. At the same time, a control signal is generated based on the determination result, and the changeover switch 5 is controlled.
[0045]
Thus, the reference data is inserted into a predetermined portion between the valid data by the changeover switch 5 to generate serial data, which is converted into parallel data by the serial / parallel conversion circuit 6 and forms an OFDM signal. A plurality of complex data to which each carrier is assigned is supplied to the OFDM modulation circuit 7.
[0046]
Each complex number output from the serial / parallel conversion circuit 6 based on the frame synchronization signal, symbol synchronization signal, carrier number count pulse signal, sampling clock signal, etc. output from the timing generation circuit 3 by the OFDM modulation circuit 7. As the data is captured, an inverse discrete Fourier transform is performed on each of these complex data, and each of these complex data on the frequency axis is converted into a baseband time-axis waveform (or intermediate frequency) on the time axis. Thereafter, the signal is supplied to the frequency conversion circuit 8, converted into a radio frequency OFDM signal, and transmitted to the receiver.
[0047]
Next, the signal processing in the OFDM modulation circuit 7 will be described in detail with reference to the schematic diagrams shown in FIGS.
[0048]
First, an outline of general signal processing in the OFDM method is described in a known document, for example, “Le Floch et al.“ Digital Sound Broadcasting to Mobile Receivers ”, IEEE Transactions on Consumer Electronics, Vol. Pp. 493-503 ".
[0049]
As is clear from this document, in the OFDM method, a plurality of effective data to be transmitted is converted into a plurality of complex data, which are developed on a frequency axis, and subjected to an inverse discrete Fourier transform (IFFT). Thus, an OFDM signal to be transmitted is generated with a baseband time axis waveform on the time axis.
[0050]
In this case, as shown in FIG. 2A, for example, if the number of carrier waves is "600" and the number of IFFT points is "1024", each valid data and reference data are in the form of complex data expanded on the frequency axis. The signal is input to the OFDM modulation circuit 7, and is converted into a baseband time axis waveform as shown in FIG. 2B by the IFFT processing of the OFDM modulation circuit 7. In FIG. 2A, carrier numbers “1” to “300” are assigned to IFFT point numbers “2” to “301”, and carrier numbers “301” to “600” are assigned to IFFT point numbers “725” to “1024”. Assign to
[0051]
Then, each carrier is modulated by a preset modulation method, for example, 16QAM, to generate an OFDM signal, and when transmitting the OFDM signal, signal points of each carrier are arranged based on transmission data as shown in FIG. Then, each carrier is modulated to generate a modulated wave so as to have an amplitude and a phase corresponding to the arrangement position, and any signal point of each carrier is transmitted as reference data for the modulated wave.
[0052]
For example, in FIG. 3, if the carrier number of a certain carrier is “m”, one of the signal points A, B, C, and D is selected according to the value of “m mod 4”, and the selected signal point is selected. Signal points are transmitted as reference data for the carrier. Here, “k mod 4” represents a remainder (remainder) obtained by dividing the integer k by “4”, and a pair of 16QAM modulation is used as an amplitude value and a phase value of a carrier for transmitting reference data. Since any one of the signal points A, B, C, and D at the corner position is selected, the value of the reference data transmitted by the carrier is always constant.
[0053]
When the reference data is transmitted for each transmission symbol, as shown in FIG. 4, the transmission symbol number is “m” and the carrier wave number is “n”, and the m-th transmission symbol is “m mod 8 = n”. a carrier that is mod 8 ", ie
(Equation 1)
m≡n (mod 8)
The reference data is transmitted on each carrier having the carrier number “n”.
[0054]
Then, the above processing is performed for each transmission symbol, and as shown in FIG. 5, an OFDM signal having a transmission frame composed of one synchronization symbol and 100 transmission symbols following the synchronization symbol is obtained. It is generated and transmitted to the receiving device side.
[0055]
<Description of configuration of receiving device>
FIG. 6 is a block diagram showing one embodiment of the receiving apparatus according to the present invention.
[0056]
The receiving apparatus 11 shown in FIG. 1 includes a received data separating circuit 12, a demodulation reference data generating circuit 13, and a valid data reproducing circuit 14, and receives a radio frequency OFDM signal transmitted from the transmitting apparatus 1. Then, after reproducing the baseband time-axis waveform, based on the reference data in the baseband time-axis waveform, the optimum demodulation reference data is determined based on the moving / fixed state of the receiving device 11, the state of the transmission path, and the like. At the same time, based on the reference data for demodulation, the amplitude and phase of the effective data in the baseband time axis waveform are determined, the value of the effective data is estimated, and this is reproduced.
[0057]
The reception data separation circuit 12 includes a frequency conversion circuit 15, a frame synchronization / symbol synchronization reproduction circuit 16, an OFDM demodulation circuit 17, a parallel / serial conversion circuit 18, a valid data / reference data switching control circuit 19, and a switch 20. After receiving a radio frequency OFDM signal transmitted from the transmitting apparatus 1 and converting the frequency of the OFDM signal to reproduce a baseband time axis waveform, reference data and valid data in the baseband time axis waveform And supplies reference data to the demodulation reference data generation circuit 13 and supplies valid data to the valid data reproduction circuit 14.
[0058]
The frequency conversion circuit 15 takes in the OFDM signal in the form of a radio frequency signal transmitted from the transmitting apparatus 1, converts the OFDM signal into a baseband time axis waveform (or an intermediate frequency), and obtains the baseband time axis waveform (or (An intermediate frequency) is supplied to a frame synchronization / symbol synchronization reproduction circuit 16 and an OFDM demodulation circuit 17.
[0059]
The frame synchronization / symbol synchronization reproduction circuit 16 takes in the baseband time axis waveform (or intermediate frequency) output from the frequency conversion circuit 15 and is included in the baseband time axis waveform (or intermediate frequency). A frame synchronizing signal, a symbol synchronizing signal, a carrier wave number count pulse signal, a sampling clock signal, and the like are reproduced and supplied to an OFDM demodulation circuit 17 and a valid data / reference data switching control circuit 19.
[0060]
The valid data / reference data switching control circuit 19 transmits a OFDM signal transmission frame based on a frame synchronization signal, a symbol synchronization signal, a carrier number count pulse signal, a sampling clock signal, and the like output from the frame synchronization / symbol synchronization reproduction circuit 16. , A control signal necessary for selecting reference data included in the designated transmission symbol is generated, and the switch 20 is switched.
[0061]
The OFDM demodulation circuit 17 takes in a baseband time axis waveform (or an intermediate frequency) on the time axis output from the frequency conversion circuit 15 and also outputs a frame synchronization output from the frame synchronization / symbol synchronization reproduction circuit 16. The baseband time axis waveform (or intermediate frequency) on the time axis is on the frequency axis by discrete Fourier transform (FFT) based on a signal, a symbol synchronization signal, a carrier wave number count pulse signal, a sampling clock signal, and the like. The data is converted into the complex data and supplied to the parallel / serial conversion circuit 18.
[0062]
The parallel-to-serial conversion circuit 18 takes in a plurality of complex data output in parallel from the OFDM demodulation circuit 17, converts this into parallel-serial data, and supplies it to a common terminal of the switch 20.
[0063]
The changeover switch 20 receives the serial data output from the parallel-to-serial conversion circuit 18 by a common terminal, and when the control signal output from the valid data / reference data changeover control circuit 19 specifies the reference data, the common terminal Is supplied to one terminal and supplied to the demodulation reference data generating circuit 13. When the control signal specifies valid data, the serial data supplied to the common terminal is supplied to the other terminal. And supplies it to the valid data reproducing circuit 14.
[0064]
The demodulation reference data generation circuit 13 includes a reception reference data memory circuit 21, a transmission line characteristic fluctuation detection circuit 22, and an average / interpolation switching average number determination / demodulation reference data calculation circuit 23. The reference data in the baseband time axis waveform output from the circuit 12 is fetched, and based on the magnitude of the amplitude value fluctuation and the phase value fluctuation of the reference data and the rate of change thereof, whether the receiving apparatus 11 is moving. , Whether the transmission path characteristics are stationary or non-stationary, etc., and based on the result of the determination, generate optimal demodulation reference data from the reference data and reproduce the effective data. Supply to the circuit 14.
[0065]
The reception reference data memory circuit 21 takes in the serial data (reference data) output from the changeover switch 20, stores the reference data, and transmits the stored reference data to the transmission line characteristic fluctuation detection circuit 22 for averaging / interpolation switching. The average number determination / demodulation reference data calculation circuit 23 is supplied.
[0066]
The transmission line characteristic fluctuation detection circuit 22 takes in the reference data output from the reception reference data memory circuit 21, detects the amplitude value and the phase value of the reference data, the fluctuation rate, and the like. The characteristics of the transmission path are determined, and the result of this determination is supplied to the average data / interpolation switching average frequency determination / demodulation reference data calculation circuit 23.
[0067]
In this case, whether the receiving device 11 is fixed based on whether the amplitude value of the reference data periodically output from the reception reference data memory circuit 21 changes or the phase value changes. , Is moving, and whether the transmission path characteristics are changing. Further, based on the rate of change of the amplitude value and the rate of change of the phase value of the reference data periodically output from the reception reference data memory circuit 21, the approximate value of the change speed of the transmission path characteristic or the moving speed of the receiver 11 is calculated. Approximate values are obtained, and these determination results are supplied to a reference data calculation circuit 23 for averaging / interpolation switching average number determination / demodulation.
[0068]
The average data / interpolation switching average frequency determination / demodulation reference data calculation circuit 23 takes in the reference data output from the reception reference data memory circuit 21 and outputs each detection result output from the transmission path characteristic fluctuation detection circuit 22. Based on each determination result, the reference data for demodulation is calculated from the reference data by setting the number at the time of averaging the reference data, selecting averaging processing / interpolation processing, and the like. Supply.
[0069]
In this case, one of the averaging process and the interpolation process is selected based on whether the transmission path characteristic is stationary or non-stationary, or whether the receiving device 11 is fixed or moving. At the same time, the number of reference data to be averaged is adjusted based on the estimated value of the change speed of the transmission path characteristic, and the reference data for demodulation is calculated from the reference data. Is done.
[0070]
The valid data reproducing circuit 14 includes a valid reception data memory circuit 24 and a received data amplitude / phase calculation circuit 25, and captures valid data in the baseband time axis waveform output from the received data separation circuit 12. On the basis of the demodulation reference data output from the demodulation reference data generation circuit 13, the amplitude and phase of the valid data are determined, the value of the valid data is estimated, and this is reproduced.
[0071]
The reception effective data memory circuit 24 takes in the serial data (effective data) output from the changeover switch 20 and supplies the stored effective data to the reception data amplitude / phase calculation circuit 25 while storing the data.
[0072]
The reception data amplitude / phase calculation circuit 25 takes in the demodulation reference data output from the demodulation reference data generation circuit 13 and the valid data output from the reception valid data memory circuit 24, and receives the demodulation reference data. Based on the data, the amplitude and phase of the effective data are determined, an estimated value of the effective data is calculated, and this is output as reproduction data.
[0073]
<Description of operation of receiving device>
Next, the operation of the receiving device 11 will be described with reference to the block diagram shown in FIG.
[0074]
First, an OFDM signal (reception signal) of a radio frequency is fetched by the frequency conversion circuit 15 and frequency-converted into a baseband time-axis waveform. Supplied to
[0075]
As a result, the frame synchronization / symbol synchronization reproduction circuit 16 reproduces a frame synchronization signal, a symbol synchronization signal, a carrier wave number count pulse signal, a sampling clock signal, and the like included in the baseband time axis waveform, which are OFDM demodulated. The control circuit 19 and the valid data / reference data switching control circuit 19 supply the frame synchronization signal, the symbol synchronization signal, the carrier number count pulse signal, the sampling clock signal, and the like. Based on this, a control signal required to select each reference data included in each transmission symbol constituting the frame of the OFDM signal is generated and supplied to the changeover switch 20.
[0076]
Further, in parallel with this operation, the OFDM demodulation circuit 17 generates a discrete signal based on a frame synchronization signal, a symbol synchronization signal, a carrier wave number count pulse signal, a sampling clock signal, etc. output from the frame synchronization / symbol synchronization reproduction circuit 16. A Fourier transform (FFT) is performed, and a baseband time axis waveform (or intermediate frequency) on the time axis output from the frequency conversion circuit 15 is expanded on the frequency axis and converted into a plurality of complex data. This is supplied to a parallel-to-serial conversion circuit 18, and the complex data is converted to serial data by parallel-to-serial conversion, and supplied to a common terminal of the changeover switch 20.
[0077]
Then, based on a control signal output from the valid data / reference data switching control circuit 19 by the changeover switch 20, the reference data in the serial data and the valid data are separated, and the reference data is stored in the reception reference data memory. The valid data is supplied to and stored in the circuit 21 and received and stored in the valid data memory circuit 24.
[0078]
Next, the reference data stored in the reception reference data memory circuit 21 is read out by the transmission line characteristic fluctuation detection circuit 22, and the magnitude of the fluctuation rate of the amplitude value and the phase value of the reference data and the speed of the fluctuation are read out. After the detection is performed, the receiving mode of the receiving device 11, the characteristics of the transmission path, and the like are determined based on the detection result, and the determination result is supplied to the average / interpolation switching average number determination / demodulation reference data calculation circuit 23. Is done.
[0079]
The reference data is read from the reception reference data memory circuit 21 by the averaging / interpolation switching average number determination / demodulation reference data calculation circuit 23, and each detection result output from the transmission path characteristic fluctuation detection circuit 22 Based on each determination result, the number setting for averaging the reference data, selection of averaging processing / interpolation processing, and the like are performed, and reference data for demodulation is calculated from the reference data. It is supplied to the calculation circuit 25.
[0080]
In this case, when it is determined that the change in the transmission line characteristic is small in a state where the reception device 11 is fixed by the transmission line characteristic change detection circuit 22, the reception device 11 is determined by the number corresponding to the change rate of the transmission line characteristic. Reference data serving as amplitude / phase reference data is read from the reference data memory circuit 21, an average value of the reference data is calculated, and reference data for demodulation is generated, which is supplied to a reception data amplitude / phase calculation circuit 25. You.
[0081]
Further, even when the receiving apparatus 11 is fixed by the transmission path characteristic variation detection circuit 22, when it is determined that the change in the transmission path characteristic is large or when it is determined that the receiving apparatus 11 is moving, The latest reference data received before the valid data to be calculated for the amplitude and phase and the first reference data received after the time are interpolated to generate reference data for demodulation. Are supplied to the received data amplitude / phase calculation circuit 25.
[0082]
The valid data is read from the reception valid data memory circuit 24 by the reception data amplitude / phase calculation circuit 25, and the demodulation reference data output from the averaging / interpolation switching average number determination / demodulation reference data calculation circuit 23 is read. , The amplitude and phase of the valid data are determined, an estimated value of the valid data is calculated, and this is output as reproduction data.
[0083]
In this case, the effective data corresponding to one certain transmission symbol number and carrier number is "D_RX”, The reference data on the transmitting device 1 side is set to“ S_TX", The demodulation reference data on the receiving apparatus 11 side is set to" S_RX”, The transmitted valid data estimate“ D_TX"
D_TX/ D_RX= S_TX/ S_RX
Becomes
D_TX= D_RX・ S_TX/ S_RX
Required by Here, these "D"_RX”,“ S_TX”,“ S_RX”,“ D_TX"Are all complex number data.
[0084]
<< Effects of Embodiment >>
As described above, in this embodiment, the transmitting device 1 inserts reference data into a predetermined portion between a plurality of pieces of valid data, converts the reference data into a radio frequency OFDM signal, transmits the OFDM signal, and transmits the OFDM signal to the receiving device 11. After receiving the OFDM signal and reproducing the baseband time-axis waveform, based on the reference data in the baseband time-axis waveform, determine the moving / fixed state of the receiving device 11, the state of the transmission path, and the like. Based on this determination result, optimal demodulation reference data is generated, and based on the demodulation reference data, the amplitude and phase of valid data in the baseband time axis waveform are determined to estimate the value of the valid data. Then, since this is reproduced, the following effects can be obtained.
[0085]
First, when there is little change in transmission path characteristics, such as in fixed reception, the average value of a plurality of received reference data is calculated to obtain the demodulation reference data. The bit error rate characteristic can be approximated to the bit error rate characteristic in the case of synchronous detection in the single carrier digital modulation method.
[0086]
Also, based on the magnitude of the amplitude value fluctuation and the phase value fluctuation of the received reference data and the fluctuation rate thereof, which state of the fixed state or the moving state of the receiving apparatus 11, whether the transmission line characteristics are stable or unstable. Determine the average value of the received reference data based on this determination result, calculate the interpolation value, or change the number of reference data to be averaged to obtain the demodulation reference data. Therefore, regardless of the receiving mode of the receiving apparatus 11 and the fluctuation state of the transmission path, the optimum value can always be obtained as the value of the reference data for demodulation. Effective data can be reproduced with a low bit error rate even in any of fixed, portable, and mobile reception, and in a case where transmission line characteristics vary greatly.
[0087]
【The invention's effect】
As described above, according to the present invention, it is possible to always obtain an optimal value as the value of the reference data for demodulation, regardless of the condition of the reception mode of the receiving apparatus or the fluctuation state of the transmission path. As a result, the bit error rate of the received data can be significantly reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a transmission device.
FIG. 2 is a schematic diagram showing an example of an inverse Fourier transform operation of the OFDM modulation circuit shown in FIG.
FIG. 3 is a schematic diagram showing an example of signal point arrangement of each carrier and an example of signal point arrangement of reference data when the OFDM modulation circuit shown in FIG. 1 performs modulation by a 16QAM modulation method.
FIG. 4 is a schematic diagram showing an example of an insertion position of reference data inserted between valid data by a switching operation of a changeover switch shown in FIG. 1;
5 is a schematic diagram showing an example of a schematic format of a transmission frame configuration of an OFDM signal transmitted from the transmission device shown in FIG. 1;
FIG. 6 is a block diagram showing one embodiment of a receiving device according to the present invention.
[Explanation of symbols]
1 transmitting device
2 Fixed reference data memory circuit
3 Timing generation circuit
4 Effective data / reference data switching control circuit
5 Changeover switch
6 Series-parallel conversion circuit
7 OFDM modulation circuit
8 Frequency conversion circuit
11 Receiver
12 Receive data separation circuit
13 Reference data generation circuit for demodulation
14. Effective data recovery circuit
15 Frequency conversion circuit
16 Frame synchronization / symbol synchronization reproduction circuit
17 OFDM demodulation circuit
18 Parallel-to-serial conversion circuit
19 Effective data / reference data switching control circuit
20 Changeover switch
21 Reception reference data memory circuit
22 Transmission line characteristic fluctuation detecting circuit (receiving state detecting means, fluctuation rate detecting means)
23 Averaging / Interpolation Switching Average Number Determination / Demodulation Reference Data Calculation Circuit
24 Receive valid data memory circuit
25 Receive data amplitude / phase calculation circuit

Claims (2)

After expanding a plurality of transmission data to be transmitted on the frequency axis, a receiving apparatus in an orthogonal frequency division multiplexing modulation and demodulation method that expands on the time axis to generate a multicarrier signal,
When restoring valid data from the transmitting side based on amplitude / phase reference data which is inserted at a predetermined position in a transmission frame and periodically transmitted as amplitude / phase reference data, a plurality of received amplitude / phase Means for calculating at least one of the average value or the interpolated value of the reference data, and obtaining reference data for demodulation used for restoring valid data;
A transmission state characteristic is stationary or non-stationary, or the receiving apparatus is stationary or receiving state detecting means for detecting whether or not moving,
Based on the detection result obtained by the reception state detecting means, the demodulation reference data used for restoring valid data is obtained by calculating an average value of a plurality of received amplitude / phase reference data, or by interpolation. Means for switching whether to obtain by calculating the value,
A receiving device comprising: The receiving device according to claim 1,
A rate of change of the transmission line characteristic, or a fluctuation rate detecting means for detecting an approximate value of the moving speed of the receiving device;
Based on the detection result obtained by the fluctuation rate detection means, to change the number of reference data to be averaged when calculating an average value of a plurality of received amplitude / phase reference data, to restore valid data Means for obtaining demodulation reference data used for
A receiving device comprising:

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